Cement compositions comprising strength-enhancing lost circulation materials and methods of cementing in subterranean formations

ABSTRACT

Cement compositions comprising a strength-enhancing lost circulation material, and methods for cementing using such cement compositions are provided. Exemplary embodiments of the cement compositions comprise cement, water, and a strength-enhancing lost circulation material. Optionally, other additives suitable for inclusion in cement compositions may be added.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to subterranean cementing operations, andmore particularly, to cement compositions comprising strength-enhancinglost circulation materials, and methods of using such cementingcompositions in subterranean formations.

2. Description of the Related Art

Hydraulic cement compositions are commonly utilized in subterraneanoperations, particularly subterranean well completion and remedialoperations. For example, hydraulic cement compositions are used inprimary cementing operations whereby pipe strings such as casings andliners are cemented in well bores. In performing primary cementing,hydraulic cement compositions are pumped into the annular space betweenthe walls of a well bore and the exterior surface of the pipe stringdisposed therein. The cement composition is permitted to set in theannular space, thereby forming an annular sheath of hardenedsubstantially impermeable cement therein that substantially supports andpositions the pipe string in the well bore and bonds the exteriorsurface of the pipe string to the walls of the well bore. Hydrauliccement compositions also are used in remedial cementing operations suchas plugging highly permeable zones or fractures in well bores, pluggingcracks and holes in pipe strings, and the like.

Subterranean formations transversed by well bores are often weak, highlypermeable, and extensively fractured. In some cases, such formations maybe unable to withstand the hydrostatic head pressure normally associatedwith fluids (e.g., cement compositions and the like) being injected intothe formation. In such cases, the hydrostatic pressure may be sufficientto force such fluids into the fractures and/or permeable zones of theformation, which may result in a significant loss of fluid into theformation. This loss of fluid circulation is problematic for a number ofreasons. For example, where the loss of circulation occurs during acementing operation, excessive fluid loss may cause a cement compositionto be prematurely dehydrated and may decrease the compressive strengthof the cement composition. Excessive fluid loss into the formation mayalso prevent or reduce bond strength between the set cement compositionand the subterranean zone, the walls of pipe, and/or the walls of thewell bore.

Previous attempts to minimize the loss of circulation into thesubterranean formation involved the addition to the cement compositionof a variety of additives including, but not limited to, asphaltines,ground coal, cellulosic, plastic materials, and the like. The additionof such additives was an attempt to plug or bridge the fractures and/orthe permeable zones in the formation where the treatment fluids aretypically lost. However, during a cementing operation, the addition ofthe lost circulation materials often has been detrimental to thecompressive strength of the cement composition because, inter alia, suchadditives do not bond to the cement. Because one function of the cementis to support the pipe string in the well bore, such reduction in thecompressive strength of the cement composition is undesirable.

SUMMARY OF THE INVENTION

The present invention relates to subterranean cementing operations, andmore particularly, to cement compositions comprising strength-enhancinglost circulation materials, and methods of using such cementingcompositions in subterranean formations.

An example of a method of the present invention is a method of cementingin a subterranean formation comprising the steps of: providing a cementcomposition comprising cement, a strength-enhancing lost circulationmaterial, and water; placing the cement composition into a subterraneanformation; and allowing the cement composition to set.

An example of a composition of the present invention is a cementcomposition comprising: cement, a strength-enhancing lost circulationmaterial, and water.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to subterranean cementing operations, andmore particularly, to cement compositions comprising strength-enhancinglost circulation materials, and methods of using such cementingcompositions in subterranean formations.

The improved cement compositions of the present invention generallycomprise cement, water, and a strength-enhancing lost circulationmaterial. Optionally, other additives suitable for use in conjunctionwith subterranean cementing operations may be added to these cementcompositions if desired. Typically, the cement compositions of thepresent invention have a density in the range of from about 4 lb/gallonto about 20 lb/gallon. In certain exemplary embodiments, the cementcompositions of the present invention have a density in the range offrom about 8 lb/gallon to about 17 lb/gallon. One of ordinary skill inthe art with the benefit of this disclosure will recognize theappropriate density of the cement composition for a chosen application.

The water utilized in the cement compositions of the present inventioncan be fresh water, salt water (e.g., water containing one or more saltsdissolved therein), brine (e.g., saturated salt water), or seawater.Generally, the water can be from any source provided that it does notcontain an excess of compounds, e.g., dissolved organics, that mayadversely affect other components in the cement composition. The densityof the water may vary based, inter alia, on the salt content. In certainexemplary embodiments, the water has a density in the range of fromabout 8.3 lb/gallon to about 9.5 lb/gallon. Further, the water may bepresent in an amount sufficient to form a pumpable slurry. In certainexemplary embodiments, the water is present in the cement compositionsin an amount in the range of from about 30% to about 180% by weight ofthe cement (“bwoc”) therein. In certain exemplary embodiments, the wateris present in the cement composition in the range of from about 40% toabout 90% bwoc therein. In certain exemplary embodiments, the water ispresent in the cement composition in the range of from about 40% toabout 50% bwoc therein. One of ordinary skill in the art with thebenefit of this disclosure will recognize the appropriate amount ofwater for a chosen application.

Any cements suitable for use in subterranean applications are suitablefor use in the present invention. In one embodiment, the improved cementcompositions of the present invention comprise a hydraulic cement. Avariety of hydraulic cements are suitable for use including thosecomprised of calcium, aluminum, silicon, oxygen, and/or sulfur which setand harden by reaction with water. Such hydraulic cements include, butare not limited to, Portland cements, pozzolana cements, gypsum cements,soil cements, calcium phosphate cements, high alumina content cements,silica cements, high alkalinity cements, and mixtures thereof.

The cement compositions of the present invention further comprise astrength-enhancing lost circulation material. The strength-enhancinglost circulation material may be any material that provides a desiredlevel of lost circulation control from the cement composition into theformation with minimal adverse impact to the compressive strength of thecement composition. Among other things, certain embodiments of thestrength-enhancing lost circulation material of the present inventionbridge and/or plug fractures and permeable zones in the formation so asto minimize loss of fluid circulation into the formation. Certainexemplary embodiments of the strength-enhancing lost circulationmaterial of the present invention have a density such that they do notrise to the surface of the well bore if circulation of the cementcomposition should cease. Generally, the strength-enhancing lostcirculation material chemically and/or mechanically bonds to the matrixof the cement. Generally, the strength-enhancing lost circulationmaterial may have any particle size distribution that provides a desiredlevel of lost circulation control. In an exemplary embodiment, thestrength-enhancing lost circulation material may have a particle sizedistribution in the range of from about 37 micrometers to about 4,750micrometers. In an exemplary embodiment, the strength-enhancing lostcirculation material is vitrified shale. A variety of vitrified shalesare suitable for use including those comprised of silicon, aluminum,calcium, and/or magnesium. In an exemplary embodiment, the vitrifiedshale may be fine grain vitrified shale whereby the fine vitrified shaleparticles may have a particle size distribution in the range of fromabout 74 micrometers to about 4,750 micrometers. An example of asuitable fine grain vitrified shale is “PRESSUR-SEAL® FINE LCM,” whichis commercially available from TXI Energy Services, Inc., in Houston,Tex. In an exemplary embodiment, the vitrified shale may be coarse grainvitrified shale whereby the coarse vitrified shale particles may have aparticle size distribution in the range of from about 149 micrometers toabout 4,750 micrometers. An example of a suitable coarse grain vitrifiedshale is “PRESSUR-SEAL® COARSE LCM,” which is commercially availablefrom TXI Energy Services, Inc., in Houston, Tex.

Generally, the strength-enhancing lost circulation material may bepresent in the cement compositions in an amount sufficient to provide adesired level of lost circulation control. In one embodiment, thestrength-enhancing lost circulation material is present in the cementcomposition in an amount in the range of from about 1% to about 50%bwoc. In certain exemplary embodiments, the strength-enhancing lostcirculation material is present in the cement composition in an amountin the range of from about 5% to about 10% bwoc. One of ordinary skillin the art with the benefit of this disclosure will recognize theappropriate amount of the strength-enhancing lost circulation materialfor a chosen application.

Optionally, the cement composition may further comprise a conventionallost circulation material. The conventional lost circulation materialmay be any material that minimizes the loss of fluid circulation intothe fractures and/or permeable zones of the formation. Conventional lostcirculation materials typically comprise a variety of materials, whichinclude, but are not limited to, asphaltines, ground coal, cellulosic,plastic materials, and the like. The conventional lost circulationmaterials may be provided in particulate form. One of ordinary skill inthe art with the benefit of this disclosure will recognize theappropriate amount of the conventional lost circulation material for achosen application.

Additional additives may be added to the cement compositions of thepresent invention as deemed appropriate by one skilled in the art withthe benefit of this disclosure. Examples of such additives include,inter alia, fly ash, silica compounds, fluid loss control additives, asurfactant, a dispersant, an accelerator, a retarder, a salt, mica,fiber, a formation conditioning agent, fumed silica, bentonite,expanding additives, microspheres, weighting materials, a defoamer, andthe like. For example, the cement compositions of the present inventionmay be foamed cement compositions wherein an expanding additive thatproduces gas within the cement composition has been added in order,inter alia, to reduce such composition's density. An example of asuitable expanding additive comprises a blend containing gypsum and iscommercially available under the tradename “MICROBOND” from HalliburtonEnergy Services, Inc. at various locations. One of ordinary skill in theart with the benefit of this disclosure will recognize the proper amountof an expanding additive to use in order to provide a foamed cementcomposition having a desired density. An example of a suitable fluidloss control additive comprises an acrylamide copolymer derivative, adispersant, and a hydratable polymer, and is disclosed in commonly ownedU.S. patent application Ser. No. 10/608,748 filed on Jul. 21, 2003, therelevant disclosure of which is hereby incorporated herein by reference.An example of a suitable fly ash is an ASTM class F fly ash which iscommercially available from Halliburton Energy Services of Dallas, Tex.under the trade designation “POZMIX® A.”

An exemplary embodiment of a cement composition of the present inventioncomprises cement, a strength-enhancing lost circulation material, andwater. An exemplary embodiment of a cement composition of the presentinvention comprises cement, vitrified shale, and water. An exemplaryembodiment of a cement composition of the present invention comprisesTexas Lehigh Premium cement, 5% PRESSUR-SEAL® FINE LCM bwoc, and 39.4%water bwoc. Another exemplary embodiment of a cement composition of thepresent invention comprises Texas Lehigh Premium cement, 5%PRESSUR-SEAL® COARSE LCM bwoc, and 39.4% water bwoc.

An exemplary embodiment of a method of the present invention comprisesproviding a cement composition that comprises cement, astrength-enhancing lost circulation material, and water sufficient toform a pumpable slurry; placing this cement composition into asubterranean formation; and allowing the cement composition to settherein. Another exemplary embodiment of a method of the presentinvention comprises providing a cement composition that comprisescement, vitrified shale, and water sufficient to form a pumpable slurry;placing this cement composition into a subterranean formation; andallowing the cement composition to set therein.

To facilitate a better understanding of the present invention, thefollowing examples of some of the preferred embodiments are given. In noway should such examples be read to limit the scope of the invention.

EXAMPLE 1

Sample cement compositions were prepared by mixing a base cement slurrywith a lost circulation material in accordance with the followingprocedure. The base cement slurry of 16.4 lb/gallon was prepared bymixing Texas Lehigh Premium cement with 39.4% water bwoc. Each samplecement composition was then prepared by mixing the base cement slurrywith 5% of a lost circulation material bwoc. Subsequently, each samplecement composition was mixed at 15,000 rpm in a Waring blender forapproximately 35 seconds. After sample preparation, a compressivestrength test was performed at 80° F. and 200° F. in accordance with APISpecification 10, RP 8.3, Recommended Practices for Testing WellCements.

Sample Cement Composition No. 1 consisted of the base cement slurry. Nolost circulation material was included. At 80° F., the compressivestrength of Sample Cement Composition No. 1 was found to be 1641 psi. At200° F., the compressive strength of Sample Cement Composition No. 1 wasfound to be 4823 psi.

Sample Cement Composition No. 2 was prepared by mixing the base cementslurry with 5% of a strength-enhancing lost circulation material bwoc.Specifically, the strength enhancing lost circulation material includedwas PRESSUR-SEAL® COARSE LCM. At 80° F., the compressive strength ofSample Cement Composition No. 2 was found to be 1591 psi. At 200° F.,the compressive strength of Sample Cement Composition No. 2 was found tobe 4351 psi.

Sample Cement Composition No. 3 was prepared by mixing the base cementslurry with 5% of a strength-enhancing lost circulation material bwoc.Specifically, the strength-enhancing lost circulation material includedwas PRESSUR-SEAL® FINE LCM. At 80° F., the compressive strength ofSample Cement Composition No. 3 was found to be 1560 psi. At 200° F.,the compressive strength of Sample Cement Composition No. 3 was found tobe 5637 psi.

Sample Cement Composition No. 4 was prepared by mixing the base cementslurry with 5% of a conventional lost circulation material bwoc.Specifically, the conventional lost circulation material included wasasphaltine. At 80° F., the compressive strength of Sample CementComposition No. 4 was found to be 1309 psi. At 200° F., the compressivestrength of Sample Cement Composition No. 4 was found to be 3749 psi.

Sample Cement Composition No. 5 was prepared by mixing the base cementslurry with 5% of a conventional lost circulation material bwoc.Specifically, the conventional lost circulation material included wasground FORMICA® material. At 80° F., the compressive strength of SampleCement Composition No. 5 was found to be 1165 psi. At 200° F., thecompressive strength of Sample Cement Composition No. 5 was found to be3140 psi.

A summary of the compressive strength demonstrated by each sample cementcomposition is depicted in Table 1, below.

TABLE 1 COMPRES- % CHANGE COMPRES- % CHANGE SIVE IN COM- SIVE IN COM-STRENGTH PRESSIVE STRENGTH PRESSIVE AT 80° F. STRENGTH AT 200° F.STRENGTH FLUID (psi) AT 80° F. (psi) AT 200° F. Sample 1641 N/A 4823 N/ACement Composition No. 1 Sample 1591  −3% 4351  −9% Cement CompositionNo. 2 Sample 1560  −5% 5637 +17% Cement Composition No. 3 Sample 1309−20% 3749 −23% Cement Composition No. 4 Sample 1165 −29% 3140 −35%Cement Composition No. 5

Thus, the above example demonstrates, inter alia, that the cementcompositions of the present invention comprising a strength-enhancinglost circulation material provide enhanced compressive strength ascompared to cement compositions comprising conventional lost circulationmaterials.

EXAMPLE 2

An additional compressive strength test was performed on another cementcomposition, Sample Cement Composition No. 6, that was prepared asfollows.

The base cement slurry of 14 lb/gallon was prepared by mixing a 65/35TXI Standard Cement/POZMIX® A blend with 93.8% water bwoc. Additionally,9.8% of PRESSUR-SEAL® COARSE LCM bwoc, 0.4% HALAD®-344 additive bwoc,0.4% bwoc of a fluid loss control additive comprising an acrylamidecopolymer derivative, a dispersant, and a hydratable polymer, 0.5%D-AIR™ 3000 bwoc, 0.1% of a free water control agent bwoc, 7% MICROBONDbwoc, and 5% NaCl by weight of water were also blended into the samplecement composition. HALAD®-344 additive is a fluid loss control additivethat is commercially available from Halliburton Energy Services, Inc.,at various locations. D-AIR™ 3000 is a defoaming agent that iscommercially available from Halliburton Energy Inc., at variouslocations.

After Sample Cement Composition No. 6 was prepared, it was pumped into awell bore at 100° F., 1,900 psi for 3 hours and 46 minutes and allowedto set therein. Next, a compressive strength test was performed at 110°F. at selected intervals over a 48 hour period in accordance with APISpecification 10, RP 8.3, Recommended Practices for Testing Well Cement.A summary of the compressive strength demonstrated by Sample CementComposition No. 6 at each interval is provided in Table 2, below.

TABLE 2 COMPRES- COMPRES- COMPRES- COMPRES- SIVE SIVE SIVE SIVE STRENGTHSTRENGTH STRENGTH STRENGTH AT 6 AT 12 AT 24 AT 48 HOURS HOURS HOURSHOURS FLUID (psi) (psi) (psi) (psi) Sample 302 852 1500 2280 CementComposition No. 6

Thus, the above example demonstrates, inter alia, that CementComposition No. 6, a cement composition of the present inventioncomprising a strength-enhancing lost circulation material, providesenhanced compressive strength.

Therefore, the present invention is well-adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

1. A method of using a strength-enhancing lost circulation material toreduce the loss of circulation of a cement composition in a subterraneanformation comprising the steps of: providing a cement compositioncomprising cement, a strength-enhancing lost circulation material, andwater, wherein the cement is selected from the group consisting ofPortland cements, pozzolana cements, gypsum cements, soil cements,calcium phosphate cements, high alumina content cements, silica cements,or high alkalinity cements; placing the cement composition into asubterranean formation; reducing the loss of circulation of the cementcomposition using the strength-enhancing lost circulation material ofsufficient size to reduce the loss of circulation of the cementcomposition; and allowing the cement composition to set.
 2. The methodof claim 1 wherein the cement composition further comprises fly ash, asurfactant, a dispersant, an accelerator, a retarder, a salt, mica,fiber, a formation conditioning agent, fumed silica, bentonite,expanding additives, microspheres, weighting materials, or a defoamer.3. The method of claim 1 wherein the cement composition has a density inthe range of from about 4 pounds per gallon to about 20 pounds pergallon.
 4. The method of claim 1 wherein the cement composition has adensity in the range of from about 8 pounds per gallon to about 17pounds per gallon.
 5. The method of claim 1 wherein the water is presentin the cement composition in an amount sufficient to form a pumpableslurry.
 6. The method of claim 5 wherein the water is present in thecement composition in an amount in the range of from about 30% to about180% by weight of the cement.
 7. The method of claim 5 wherein the wateris present in the cement composition in an amount in the range of fromabout 40% to about 50% by weight of the cement.
 8. The method of claim 1wherein the cement comprises a hydraulic cement.
 9. The method of claim1 wherein the strength-enhancing lost circulation material comprisesvitrified shale.
 10. The method of claim 9 wherein the vitrified shaleis fine grain.
 11. The method of claim 9 wherein the vitrified shale iscoarse grain.
 12. The method of claim 1 wherein the strength-enhancinglost circulation material has a particle size distribution in the rangeof from about 37 micrometers to about 4,750 micrometers.
 13. The methodof claim 1 wherein the strength-enhancing lost circulation material hasa density such that the strength-enhancing lost circulation materialdoes not rise to the surface of the well bore if circulation of thecement composition should cease.
 14. The method of claim 1 wherein thestrength-enhancing lost circulation material is present in the cementcomposition in an amount in the range of from about 1% to about 50% byweight of the cement.
 15. The method of claim 1 wherein thestrength-enhancing lost circulation material is present in the cementcomposition in an amount in the range of from about 5% to about 10% byweight of the cement.
 16. The method of claim 1 wherein thestrength-enhancing lost circulation material chemically bonds to thecement.
 17. The method of claim 16 wherein the strength-enhancing lostcirculation material mechanically bonds to the cement.
 18. The method ofclaim 1 wherein the strength-enhancing lost circulation materialmechanically bonds to the cement.
 19. The method of claim 1 wherein thestrength-enhancing lost circulation material enhances the lostcirculation control characteristics and/or the compressive strength ofthe cement composition.
 20. The method of claim 1 wherein the cementcomposition further comprises a conventional lost circulation material.21. The method of claim 1 wherein the cement composition furthercomprises a fluid loss control additive.
 22. The method of claim 21wherein the fluid loss control additive comprises an acrylamidecopolymer derivative, a dispersant, and a hydratable polymer.
 23. Themethod of claim 1 wherein water is present in the cement composition inan amount in the range of from about 40% to about 50% by weight of thecement; wherein the strength-enhancing lost circulation material ispresent in the cement composition in an amount in the range of fromabout 5% to about 10% by weight of the cement; wherein thestrength-enhancing lost circulation material is vitrified shale; whereinthe vitrified shale has a particle size distribution in the range offrom about 37 micrometers to about 4,750 micrometers; and wherein thecement composition has a density in the range of from about 4 pounds pergallon to about 20 pounds per gallon.
 24. A method of cementing in asubterranean formation comprising the steps of: providing a cementcomposition comprising: cement, vitrified shale, and water, wherein thecement is selected from the group consisting of Portland cements,pozzolana cements, gypsum cements, soil cements, calcium phosphatecements, high alumina content cements, silica cements, or highalkalinity cements; placing the cement composition into a subterraneanformation; using the vitrified shale to reduce the loss of cementcomposition into the subterranean formation; and allowing the cementcomposition to set.
 25. The method of claim 24 wherein the cementcomposition further comprises fly ash, a surfactant, a dispersant, anaccelerator, a retarder, a salt, mica, fiber, a formation conditioningagent, fumed silica, bentonite, expanding additives, microspheres,weighting materials, or a defoamer.
 26. The method of claim 24 whereinthe cement composition has a density in the range of from about 4 poundsper gallon to about 20 pounds per gallon.
 27. The method of claim 24wherein the cement composition has a density in the range of from about8 pounds per gallon to about 17 pounds per gallon.
 28. The method ofclaim 24 wherein the water is present in the cement composition in anamount sufficient to form a pumpable slurry.
 29. The method of claim 28wherein the water is present in the cement composition in an amount inthe range of from about 30% to about 180% by weight of the cement. 30.The method of claim 28 wherein the water is present in the cementcomposition in an amount in the range of from about 40% to about 50% byweight of the cement.
 31. The method of claim 24 wherein the cementcomprises a hydraulic cement.
 32. The method of claim 24 wherein thevitrified shale is fine grain.
 33. The method of claim 24 wherein thevitrified shale is coarse grain.
 34. The method of claim 24 wherein thevitrified shale has a particle size distribution in the range of fromabout 37 micrometers to about 4,750 micrometers.
 35. The method of claim24 wherein the vitrified shale has a density such that the vitrifiedshale does not rise to the surface of the well bore if circulation ofthe cement composition should cease.
 36. The method of claim 24 whereinthe vitrified shale is present in the cement composition in an amount inthe range of from about 1% to about 50% by weight of the cement.
 37. Themethod of claim 24 wherein the vitrified shale is present in the cementcomposition in an amount in the range of from about 5% to about 10% byweight of the cement.
 38. The method of claim 24 wherein the vitrifiedshale chemically bonds to the cement.
 39. The method of claim 38 whereinthe vitrified shale mechanically bonds to the cement.
 40. The method ofclaim 24 wherein the vitrified shale mechanically bonds to the cement.41. The method of claim 24 wherein the vitrified shale enhances the lostcirculation control characteristics and/or the compressive strength ofthe cement composition.
 42. The method of claim 24 wherein the cementcomposition further comprises a conventional lost circulation material.43. The method of claim 24 wherein the cement composition furthercomprises a fluid loss control additive.
 44. The method of claim 43wherein the fluid loss control additive comprises an acrylamidecopolymer derivative, a dispersant, and a hydratable polymer.
 45. Themethod of claim 24 wherein water is present in the cement composition inan amount in the range of from about 40% to about 50% by weight of thecement; wherein the vitrified shale is present in the cement compositionin an amount in the range of from about 5% to about 10% by weight of thecement; wherein the vitrified has a particle size distribution in therange of from about 37 micrometers to about 4,750 micrometers; andwherein the cement composition has a density in the range of from about4 pounds per gallon to about 20 pounds per gallon.